null mysql

1.UPPER and UCasereturns the string str, which changes all characters to uppercase based on the current character set mapping (the default is Iso-8859-1 Latin1). This function is reliable for multiple bytes. 2.LOWER and LCasereturns the string str,

1. Description of the problemUse database query statement "ALTER TABLE information modify ' number ' varchar (255) NOT NULL ' because you want to change the" number "column in the" Information "table to non-null You can change the other columns, but

There are a variety of MySQL character sets, the following is a list of three of the most common MySQL character set viewing methods, this method for your reference, I hope you learn MySQL database can be enlightened.One, view MySQL database server

A string or series (string) is a finite sequence of 0 or more characters. Generally recorded as s= ' a1a2 an ' (n>=0). It is the data type that represents text in the programming language. A string is usually used as an action object, such as

In the MySQL database, DDL operations on a table that has been created, such as adding a field. During the test, the DDL operation was found to be exceptionally long. Oracle, usually only modify the data dictionary can be, the operation time is very

Data Type Basic Introduction Numeric type整形类型：tinyint,int,bigint浮点类型：float,double String typechar系列：char varchartext系列：textblob系列：blob枚举类型：ENUM集合类型：SET Time Date Typedate time datetime timestamp year tinyint and int plastic testingmysql>

About MySQL ifnull functionsThe MySQL IFNULL function is one of the MySQL control flow functions that accepts two parameters, and if not NULL , returns the first argument. Otherwise, the IFNULL function returns a second argument.Two parameters can

About MySQL for Boolean and tinyint (1)Boolean typeMySQL saves a Boolean value with 1 for true,0 representing False,boolean in MySQL with type tinyint (1),There are four constants in MySQL: True,false,true,false, which represent 1,0,1,0 respectively,

MySQL's engine:InnoDB: Features a row lock design, supports foreign keys, and supports non-locking reads similar to Oracle, where the default read operation does not generate locks. The default storage engine above mysql5.5.8MyISAM: Does not support

1.unix_timestampConverts a time into a timestamp. (date type data converted to timestamp form integer)Time stamp of the current time without passing the time parameterMysql> select Unix_timestamp ();+------------------+| Unix_timestamp () |+---------

Frequently used MySQL commands to change the table structure of some SQL statements, including adding, deleting, modifying fields, adjusting the order of the fields.To add a field:ALTER TABLE ' User_movement_log ' Add column Gatewayid int not NULL

1. Description:The first is to prepare two servers, one master server (master), the other from the server (Slave), and then to ensure that the master and Slave version of the same and master can not be higher than Slave version, it is generally

MySQL comes with tool use introduction:1) MySQL command: MySQL command is the most used command tool, providing users with a command line interface to operate the server to manage MySQL.Command format:Usage:mysql [Options][database]Example: Mysql-e "

1. Introduction:Zabbix MySQL plug-in to monitor the MySQL database, but too simple, basically no role, so need to do more detailed monitoring, and Percona has this detailed monitoring of the template and script, just take it.Percona Official website:

1. Create a databaseCreate DatabaseVueblog; Usevueblog;/* Create administrator table for background login, field for admin number (self-growth), account, password, logon time * /Create Table if not existsAdmin (IDintAuto_incrementPrimary Key,

Open mysql:mysql-hlocalhost-uroot-p PasswordNext is the high energy, sometimes because of the MySQL version of the problem, the problem of the field, the problem of the space is often caused by errors, so some of the following code in your machine

about MySQL database optimizationIn my humble opinion, the database is optimized to optimize storage and query speedAt present the main optimization I think is to optimize the query speed, query speed, improve the user's experienceI think that the

One, key words:1) Left (connection type) join on (condition)two, common connections:1) Join (acquisition of a Cartesian product),SELECT * from T_table1 join T_table2;2) Left connection (two table associations, after matching criteria, left table

Database Backup Introduction:Once the database has deleted the data, it will disappear forever. Therefore, DELETE you should back up the database before executing the statement, just in case you want to retrieve the deleted data.MySQL provides a

one, key and primary key differenceCREATE TABLE Wh_logrecord (logrecord_id Int (one) not NULL auto_increment,user_name varchar (+) default NULL,operation_time datetime default NULL,logrecord_operation varchar (+) default NULL,PRIMARY KEY